Plasma generating device

ABSTRACT

An improved high current plasma generating device generally comprised of an annular shaped anode means disposed in radially outward and circumjacent spaced relation to a plurality of electron emitter elements so as to cause a gaseous medium upon introduction into the discharge chamber of the device to be progressively formed into a more useful and homogeneous plasma of substantially uniform ion current density in transverse section for enhancing the fueling of a thermonuclear reactor.

United States Patent 1191 [11] 3,846,668 Ehlers et al. Nov. 5, 1974 [5PLASMA GENERATING DEVICE 3,614,440 10/1971 Carr 315/111 Inventors:Kenneth w. Ehlers Alamo; wulf B. 3,760,225 9/1973 Ehlers et a1 313/63KklBkl,bthfCl'f. er 6 ey O o al Primary ExaminerRonald L. W1bertAsslgneei The Umted States of America as Assistant Examiner-Richard A.Rosenberger p y the f q States Attorney, Agent, or FirmJohn A. Horan;Frederick Atom c Energy Commission, Robertson Washmgton, DC.

[22] Filed: Feb. 22, 1973 57 ABSTRACT [2]] Appl- N05 334,824 An improvedhigh current plasma generating device generally comprised of an annularshaped anode 521 11.5. cu 315/111, 250/423, 313/63, means disPosed inradially Outward and Circumjacem 3 2 spaced relation to a plurality ofelectron emitter ele- 511 Int. Cl 1101 7/24, 110511 1/00 mems so as tocause a gaseous medium p introduc- [58] Field of Search 313/63 230-315/111- tion into the discharge Chamber of the device to be 56progressively formed into a more useful and homogeneous plasma ofsubstantially uniform ion current den- 56] References Cited sity intransverse section for enhancing the fueling of a UNITED STATES PATENTSthermonuclear reactor. 3,345,820 10/1967 Dryden 315/111 6 Claims, 2Drawing Figures MASTER CONTROL PATENTEDnnv 5|974 mm m 2 3L846668 MHSTEREiEl- PLASMA GENERATING DEVICE Reference is made to the copending pat.application entitled, High Current Ion Source by Kenneth W. Ehlers etal, filed June 6, 1972, and having S.N. 260,236, now US. Pat. No.3,760,225, issued Sept. 18, 1973.

BACKGROUND OF THE INVENTION The invention was conceived or made in thecourse of Contract No. W-7405-ENG-48 with the United States AtomicEnergy Commission.

This invention'relates to a plasma generating device. More particularly,it relates to an improved high current plasma generating device forproducing a stable and quiescent plasma of substantially uniform ioncurrent density. I

In the past various plasma generating devices have been designed asexemplified by two US. Pat. Nos. 2,785,31 l to Lawrence and 2,902,614 toBaker and the aforementioned copending US. application. Prior ionproducing devices were incapable of generating plasmas that wouldsatisfactorily meet the overall fuel requirements for a thermonuclearreactor without encountering various difficulties such as nonhomogeneityof an ion beam as it was extracted from the plasma generating device,excessive optical convergence or divergence of the extracted ion, etc.

This invention relates to an improved plasma generating device generallycomprised of a plurality of electron emitter filaments and an annularshaped anode disposed in outwardly spaced and circumjacent relation tothe plurality of emitter elements so as to cause a gaseous medium uponintroduction into the discharge chamber of the device to beprogressively formed into a homogeneous plasma for effecting fueling ofthe thermonuclear reactor with minimal difficulties.

Accordingly, it is an object of the present invention to provide animproved plasma forming device that will effect the production of aplasma having a stable and substantially uniform ion current density intransverse section upon operating the present device at are currents upto and on the order of I000 amperes.

Another object of the instant invention is to provide an improved plasmaforming device having an annularshaped anode surface area for minimizingamong other things the adverse effects of an anode sheath build-uphaving the tendency to cause accelerated wear and overheating of theinstant device.

SUMMARY OF THE INSTANT INVENTION The present invention relates to animproved plasma generating device generally comprised of a plurality ofelectron emitter elements and a novel annular shaped anode disposed inradially outward and circumjacent spaced relation to the emitterelements for effecting ionization of a gaseous medium made-up of variousselected atomic compositions into an ionized plasma of substantiallyuniform ion current density, such uniform ion density effectingformation of an improved fuel for a thermonuclear reactor.

IE E CR TI OF TEEQBAMNQS...

FIG. 1 is a schematic and sectional view in dotted and solid lines of aplasma generating device that incorporates a preferred embodiment of theinstant invention; and

FIG. 2 is a graphic view of the radial profile of the ion currentdensity of more than one plasma produced by the present inventivedevice.

With continued reference to the drawings they illustrate a preferredembodiment of an improved plasma generating device 10 for introducingand subjecting a given pulsed volume of a gaseous medium to a relativelyhigh are current range so as to cause formation of the introducedgaseous medium into a pulse type plasma of substantially uniform ioncurrent density the ions of which can be extracted for fueling athermonuclear reactor in improved fashion. Although the instant deviceis preferably operated to produce a plasma in pulse-type fashion it isnot intended to be limited thereto. Device 10 is generally comprised ofa hollow cylindrical shaped vessel made up of uniquely interconnectedelements so as to define a vacuum electron arc discharge and plasmaforming chamber 14. A master control electric pulse and operatingcircuit 16 and a pressurized gaseous source 18 for timely supplying aselected amount of a gaseous medium to be ionized in chamber 14 areassociated with device 10 in the manner shown in FIG. 1. An ionaccel-decel extraction grid 20 is connected to the right or outlet endof decive 10 as illustrated in FIG. 1 for extracting and accelerating aplurality of ions from a plasma formed in chamber 14 to grid 20 while atthe same time focussing the extracted and accelerated ions in theconfiguration of an ion beam of improved collimated shape from grid 20to the containment zone of a thermonuclear reactor (not shown) such as,e.g., a 2X-ll type or Baseball type of thermonuclear reactor all duringoperation of device 10. As will become more fully apparent hereinafterbecause of the device creating a plasma of substantially uniform ioncurrent density as well as forming a improved ion beam from the plasmacreated, a thermonuclear reactor can be fueled in a more efficientfashion.

In an advantageous embodiment of the present invention, device 10 iscomprised of a vessel having an mused TifillPEBiEPJZEIIS paitgi spa ialy aligned intermediately disposed annular ring elements 26 and 28. Sincethe inner annular surface 25 of ring 26 preferably serves as the anodeof the present device, ring 26 is electrically connected to mastercontrol 16 by way of electric lead 27.

As indicated in FIG. 1, the inner opposed wall portions of end cap 22and ring 26 and rings 26 and 28, are provided with opposed and matching0-ring receiving grooves. Upon inserting an 0-ring 29 in an 0-ringreceiving groove of a given vessel element, e.g., ring 26 inconventional fashion, it is to be understood that the 0-ring hassufficient thickness such that upon assembling the rings 26 and 28 andend cap 22 together to form the right vessel end of device 10, theopposed inner end faces of rings 26 and 28 and ring 26 and end cap 22are held in spaced relation to each other. At the same time an O-ring isinserted in a groove between rings 26 and- 28 and between end cap 22 andring 26, the outer opposed and matching stepped and recessed portions ofrings 26 and 28 and ring 26 and end cap 22 are provided with anelastomeric seal ring 30 clampingly held therebetween in the mannershown in FIG. 1. Seal ring 30 is preferably composed of a suitable radeiszv rxmat nalharinsap tqrai e he t e i tance and dielectric properties.

In another advantageous embodiment of the present invention, vesselincludes a plurality of thermionic electron emitter elements 36 mountedat the left end thereof in unique relation to anode ring 26. Each one ofthe emitter elements 36 is of corresponding hairpin or U-shapedconfiguration and is preferably composed of a suitable grade ofrefractory tungsten material of wire-like configuration that normallyhas a diameter on the order of a half millimeter.

An inner chuck assembly includes an annular plate 38 and a series ofplug-shaped molybdenum chucks 39 only one of the chucks 39 being shownfor the sake of brevity in FIG. 1. Each one of the chucks 39 isthreadably connected to one end face of plate 38 is equally spacedcircumferential relation to the other chucks. An outer chuck assembly atthe left end of device 10 includes an annular plate 40 and a series ofplug-shaped molybdenum chucks 41 only one of the chucks 41 being shownfor the sake of brevity in FIG. 1. For reasons apparent hereinafterchuck 41 has a longer length than chuck 39. As with chucks 39, each oneof the chucks 41 is threadably connected to one end face of plate 40 inequally-spaced and circumferential relation to the other chucks 41.

Inner chuck plate 38 is provided with a series of apertures 42interposed between the series of chucks 39 in equally spaced andcircumferential relation to each other and the series of chucks 39. Eachone of the apertures 42 in plate 38 freely receives a given chuck 41upon assembly of plates 38 and 40 together in the manner shown inFIG. 1. A spacer ring 44 is provided with a series of apertures 46 forfreely receiving the outer ends of the alternate series of chucks 39 and41 upon assembly of spacer ring 44 to previously assembled inner andouter plates 38 and 40. As with annular rings 26 and 28, an annular seal48 of epoxy material is inserted between opposed faces of plates 38 and40 and plate 38 and ring 44 during assembly of plates 38 and 40 and ring44 as depicted in FIG. 1.

Prior to connection of spacer ring 44 to ring 28, the opposed ends ofeach one of the hairpin-shaped emitter elements 36 is appropriatelyconnected to its respective chuck 39 or 41. Upon connecting each one ofthe emitter elements 36 to its respective chuck 39 or 41, ring 44 isconnected to ring 28 whereby the series of circumferentially spacedemitter elements 36 extend longitudinally of vessel 10 in chamber 14 andare disposed radially inward of vessel rings 26 and 28 in circumjacentspaced relation thereto. Rings 28 and 44 are provided with opposed andmatching grooves for receiving an O-ring 29 as well as opposed andmatching stepped and recessed portions for receiving an annular seal 30.The particular manner, such as bolt nut assemblies, etc., for effectingconnection of plates 38 and 40, rings 26, 28 and 44 and end cap 22 toform vessel 10 have not been shown for the sake of simplicity in FIG. 1.Electric leads 48' and 50 extend between plates 38 and 40 and mastercontrol 16 thereby electrically connecting elements 36 in parallelfashion across master control 16.

A stem-shaped cap 52 closes off the left end of vessel 10 uponassembling cap 52 to ring 44. Prior to assembling cap 52 in thecounterbored aperture of ring 44, an annular seal 54 of epoxy materialis inserted between the opposed shoulders of the cap and ring 44.

Cap 52 and ring 44 as well as cap 22 and ring 28 are structural membersonly, defining wall and end portions of chamber 14, and are allowed tofloat electrically. It is to be understood that these metal elements ofvessel 10 may, if it is desired, also be electrically connected tomaster control 16 for selectively applying a voltage to section 22, ring28, etc. Such selective application of a voltage potential to ring 22,e.g., effectively minimizes the side capacitance effects that wouldotherwise normally occur during operation of device 10. Although mastercontrol 16 is schematically shown, it is believed that the variouscircuits for applying the proper voltages across emitter elements 36,anode ring 26, etc., are believed to be within the skill of an electriccircuit designer.

A pressurized ionizable gas source 18 is interconnected to thefully-bored-through-stem portion of cap 52 by way of conduit 56. Anelectric lead 58 interconnects source 18 and master control 16 whereby atimely signal from the control triggers a valve (not shown) fortransmitting a selected amount of ionizable gaseous medium from thesource to the electron arc discharge vacuum chamber 14 of device 10during operation of device 10. Depending upon the particular fuelrequirements for a thermonuclear reactor, source 18 can be filled withvarious gaseous mediums such as hydrogen, deuterium, tritium and variousadmixtures thereof.

Another advantageous embodiment of the present invention, device 10 iscomprised of an ion accel-decel extraction grid 20 for effectingextraction, acceleration and focussing of ions from a plasma formed indevice 10 to the containment zone of a thermonuclear reactor (notshown). Grid 20 is comprised of an outer openended sleeve 60, the leftflanged end of which is suitably connected to the apertured end cap 22of device 10. The right flanged end of sleeve 60 (not shown) isconnected to the fuel inlet port (also not shown) of a thermonuclearreactor. A grid assembly 62 is mounted within the interior of sleeve 60and is preferably made up of a series of three parallel spaced gridelements 64, 66 and 68. Each grid element 64, 66 or 68 is separatelyconnected to the master control by way of electric leads 70, 72 and 74.A given grid 64, 66 or 68 includes a series of longitudinally extendingslots 76 across the width thereof disposed in axial alignment withrespect to the series of slots of the other grid elements.

Since the inner annular anode surface 25 of ring 26 presents an extendedanode surface area each one of the series of electrons emitted from theplurality of emitter elements 36 travels from its respective element toa certain surface portion of anode ring 26 without resulting in anexcessive concentration of electrons about the anode ring duringoperation of the present device. It has been found that reducing theexcessive concentration of electrons traveling from emitter elements 36to anode ring 26 not only reduces the buildup of cathode spots adjacentto anode ring 26 but also effectively minimizes the build-up of an anodesheath or voltage gradient adjacent thereto. Reduction in the adverseeffects of cathode spots and anode sheaths assures the formation of ahomogeneous plasma as produced from a given pulse of gaseous mediumintroduced into vacuum chamber 14 when the instant device is operating.Moreover, in reducing the cathode spots the series of electrons intraveling from the plurality of emitters 36 to the anode surface 25 areincapable of forming magnetic fields, commonly known as theta fields,that produce instable plasma hash effects as indicated by the zig-zagdotted line waveform 68 in FIG.

Upon forming a plasma in chamber 14 of device 10, control 16 can applyselective voltage potentials across grids 64, 66 and 68. For instancegrid 64 could have a voltage potential of +20 kilovolts, grid 66 avoltage potential of 5 kilovolts and grid 68 a ground potential. Sincethe uniquely shaped anode 26 of device effects formation of asubstantially homogeneous plasma, for instance, a plasma formed from anH or D (hydrogen or deuterium) gaseous medium as indicated by therelatively flat H and D waveforms in FIG. 2 upon moving plasma ioncurrent sensing probe 78 in FIG. 1, grid 64 will effect extraction andacceleration of ions from the plasma in the chamber 14 of device 10 tothe interior of grid 20. At the same time grid will also be able touniformly focus various portions of the extracted and accelerated ionsof substantially uniform current density from chamber 14 of device 10into a plurality of collimated ion beams 80 that are directed throughtheir associated axially aligned slots of grids 64, 66 and 68 asindicated by dotted lines in FIG. 1. In the absence of device 10 forminga homogeneous plasma as aforedescribed, grid 20 would form an ion beamhaving convergent and/or divergent shapes 82 and 84 thereby resulting inloss of ions for fueling a thermonuclear reactor. Hence the instantdevice 10 provides minimal loss of ions thereby assuring a resultant ionbeam of maximum density for fueling a thermonuclear reactor.

In an operative embodiment of device 10 the inner surface of anode ring26 had a diameter on the order of 14 centimeters, a plurality of 20filaments 36 had an average perimeter diameter on the order of 13.50centimeters and the grid outlet opening of vessel 10 had a diameter onthe order of 13 centimeters. In operating device 10 at pulse linevoltages on the order of 40 to 300 volts and are voltages on the orderof 35-100 volts, a stable deuterium plasma was formed having an ioncurrent density of 0.5 amperes per square centimeter, with variations incurrent density on the order of 5.0 percent, when the arc current ofdevice 10 was on the order of a 1000 amperes as depicted in FIG. 2.

Similarly, another plasma essentially composed of hydrogen ions had ahomogeneous ion current density on the order of 0.3 amperes per squarecentimeter, with variations in density on the order of :5.0 percent, asindi cate d by the relatively flat waveform in FIG. 2 where the arccurrent of device 10 was on the order of 600 amperes.

In view of the foregoing embodiments of the instant inventionmodification may be made therein without departing from the presentinvention as covered by the appended claims, wherein:

What we claim is:

l. A high current plasma generating device comprising a vessel meanshaving an evacuated electron arc discharge chamber therein, an electronemitter means being made up of a plurality of refractory metalfilaments, each one of said plurality of metal filaments beingindividually mounted at one end of said vessel means so as to projectlongitudinally into the are discharge chamber and to be disposed incircumferentially spaced relation to each other as well as inwardlyspaced relation to the surrounding outer peripheral wall of said vesselmeans, reservoir means for selectively introducing a predeterminedamount of a gaseous medium to be ionized into the discharge chamber ofsaid vessel means, and an annular shaped anode means provided in theouter wall of said vessel means in outwardly spaced and circumjacentrelation to said plurality of electron emitter means for causing aseries of electron arc discharges between said plurality of electronemitter means and said anode means so as to effect formation of theintroduced amount of gaseous medium into a relatively stable andquiescent high current plasma of substantially uniform ion currentdensity throughout its extent upon simultaneous electric energization ofsaid anode means and said plurality of emitter means when said reservoirmeans admits a predetermined amount of gaseous medium into the dischargechamber.

2. A plasma generating device as set forth in claim 1 in which a givenemitter means is of hairpin shaped configuration.

3. A plasma generating device as set forth in claim 1 in which a givenemitter means is essentially composed of a refractory metal materialsuch as a suitable grade of tungsten.

4. A plasma generating device as set forth in claim 1 wherein saidvessel means has an outlet opening at the end opposing said one endwhere filaments are mounted and said plasma generating device includesmeans connected to said vessel means at said outlet opening forextracting and accelerating the ions of a plasma from the dischargechamber of said vessel means to the inlet port of a thermonuclearreactor while at the same time focusing the extracted and acceleratedions into the shape of a collimated ion beam for injection into theinlet port of a thermonuclear reactor.

-5. A plasma generating device as set forth in claim 1 in which saidreservoir means includes a gaseous medium selected from the group ofhydrogen, deuterium, tritium and various admixtures thereof.

6. In a high current plasma generating device made up of a vessel meansand a plurality of electron emitter elements mounted at one end of saidvessel means and disposed in the evacuated electron arc dischargechamber therein, each one of said elements being disposed incircumferentially spaced relation to each other and extendinglongitudinally into the chamber of said vessel means, a reservoir meansfor introducing a predetermined amount of a gaseous medium into thechamber of said vessel means, and an anode means disposed in electronarc discharge relation to said emitter means, the improvement comprisingan annular shaped anode means provided in the outer peripheral wall ofsaid vessel means and disposed in radially outward and circum- 5 5jacent spaced relation to said plurality of emitter elements so as tocause an introduced amount of gaseous medium in the chamber to be formedinto a relatively stable and quiescent high current plasma ofsubstantially uniform ion current density throughout its extent uponsimultaneous electric energization of said anode means and saidplurality of emitter means when said reservoir means admits apredetermined amount of gaseous medium to be ionized into thedischargechamber.

1. A high current plasma generating device comprising a vessel meanshaving an evacuated electron arc discharge chamber therein, an electronemitter means being made up of a plurality of refractory metalfilaments, each one of said plurality of metal filaments beingindividually mounted at one end of said vessel means so as to projectlongitudinally into the arc discharge chamber and to be disposed incircumferentially spaced relation to each other as well as inwardlyspaced relation to the surrounding outer peripheral wall of said vesselmeans, reservoir means for selectively introducing a predeterminedamount of a gaseous medium to be ionized into the discharge chamber ofsaid vessel means, and an annular shaped anode means provided in theouter wall of said vessel means in outwardly spaced and circumjacentrelation to said plurality of electron emitter means for causing aseries of electron arc discharges between said plurality of electronemitter means and said anode means so as to effect formation of theintroduced amount of gaseous medium into a relatively stable andquiescent high current plasma of substantially uniform ion currentdensity throughout its extent upon simultaneous electric energization ofsaid anode means and said plurality of emitter means when said reservoirmeans admits a predetermined amount of gaseous medium into the dischargechamber.
 2. A plasma generating device as set forth in claim 1 in whicha given emitter means is of hairpin shaped configuration.
 3. A plasmagenerating device as set forth in claim 1 in which a given emitter meansis essentially composed of a refractory metal material such as asuitable grade of tungsten.
 4. A plasma generating device as set forthin claim 1 wherein said vessel means has an outlet opening at the endopposing said one end where filaments are mounted and said plasmagenerating device includes means connected to said vessel means at saidoutlet opening for extracting and accelerating the ions of a plasma fromthe discharge chamber of said vessel means to the inlet port of athermonuclear reactor while at the same time focusing the extracted andaccelerated ions into the shape of a collimated ion beam for injectioninto the inlet port of a thermonuclear reactor.
 5. A plasma generatingdevice as set forth in claim 1 in which said reservoir means includes agaseous medium selected from the group of hydrogen, deuterium, tritiumand Various admixtures thereof.
 6. In a high current plasma generatingdevice made up of a vessel means and a plurality of electron emitterelements mounted at one end of said vessel means and disposed in theevacuated electron arc discharge chamber therein, each one of saidelements being disposed in circumferentially spaced relation to eachother and extending longitudinally into the chamber of said vesselmeans, a reservoir means for introducing a predetermined amount of agaseous medium into the chamber of said vessel means, and an anode meansdisposed in electron arc discharge relation to said emitter means, theimprovement comprising an annular shaped anode means provided in theouter peripheral wall of said vessel means and disposed in radiallyoutward and circumjacent spaced relation to said plurality of emitterelements so as to cause an introduced amount of gaseous medium in thechamber to be formed into a relatively stable and quiescent high currentplasma of substantially uniform ion current density throughout itsextent upon simultaneous electric energization of said anode means andsaid plurality of emitter means when said reservoir means admits apredetermined amount of gaseous medium to be ionized into the dischargechamber.